1. Field of the Invention
The present invention relates to a waveguide structure and an optical device that propagate surface plasmon waves.
2. Related Background Art
In the present technical field, focusing mechanisms, such as that described in Tsutomi Ishi, et al., “Si Nano-Photodiode with a Surface Plasmon Antenna,” Japanese Journal of Applied Physics, 2005, Vol. 44, No. 12, pp. L364-L366 and making use of surface plasmons, have been known from before. With the art described in Tsutomi Ishi, et al., “Si Nano-Photodiode with a Surface Plasmon Antenna,” Japanese Journal of Applied Physics, 2005, Vol. 44, No. 12, pp. L364-L366, a metal film, having one or more apertures and having a periodically varying surface, is disposed on a Si mesa structure. Of light made incident on the metal film, only wavelength components in a specific relationship with the period formed on the metal film are reinforced and transmitted to the Si mesa structure side of the apertures. This occurs due to the light energy illuminated on the metal film outside the apertures being concentrated toward the apertures via surface plasmon propagation.
As another known art of the present technical field, Japanese Published Unexamined Patent Application No. 2004-213000 describes propagation of surface plasmons using a conductive film, formed of gold, etc., with a periodic surface shape and having apertures of a size no more than a wavelength.